Components, in particular those which are used in portable communication devices, are subject to a lasting trend toward miniaturization. They include components which have mechanically or electromechanically active structures. If the spatial distances between these structures shrink, then the risk of mutual influencing increases.
Furthermore, it is often desired to separate such functional structures spatially or hermetically from their environment.
The article “High Performance Stacked Crystal Filters for GPS and Wide Bandwidth Applications” by K. M. Lakin et al. (IEEE 2001 Ultrasonic Symposium Paper 3E-6; Oct. 9, 2001) discloses SCFs (SCF=Stacked Crystal Filter) which operate with BAWs (BAW=Bulk Acoustic Wave) and comprise, stacked one above another, layers of a piezoelectric material in which bulk acoustic waves are excitable. In this case, the two layers are acoustically coupled to one another, resulting in characteristic electrical properties.
The article “Wide Bandwidth Thin Film BAW Filters” by K. M. Lakin et al. (Paper U4D-1 IEEE UFFC Aug. 25, 2004) discloses RF filters which operate with bulk acoustic waves, wherein two piezoelectric layers are arranged one directly above the other or are connected to one another via a coupling layer.
The article “Bulk Acoustic Wave Resonators and Filters for Applications Above 2 GHZ” by K. M. Lakin (MTT-S 2002 Paper THID-6 Expanded) likewise discloses RF filter structures comprising coupled piezoelectric layers in which bulk acoustic waves are capable of propagation.
The U.S. Pat. No. 7,522,020 B2 discloses filter components operating with GBAWs (GBAW=Guided Bulk Acoustic Wave), wherein electrode structures are arranged at an underside and on a top side of a substrate.
What is generally problematic about known components which have mechanically or electromechanically active structures and which are intended to be suitable for being constructed with small dimensions in accordance with the ongoing trend toward miniaturization is the mechanical coupling between precisely these functional structures.